1,721,054 research outputs found
A thermodielectric analyzer to measure the freezing and moisture characteristic of porous media
No full textThe freezing and moisture characteristics of porous media are difficult to measure. We have designed an instrument to measure the freezing characteristic of a porous medium in the range -20 to 0°C. Because of the similarity between the freezing characteristic and the moisture characteristic, the data obtained can be used to infer the moisture characteristic from about -30 to -23,600 J kg-1. Temperatures and unfrozen water contents are measured with a thermistor and a spiral-shaped transmission line connected to an oscillator, respectively. Temperatures are converted to water potential using the Clapeyron equation. Experimental results obtained with the freezing technique were compared with vapor pressure methods. The four test media used, a silt loam soil, a silty-clay loam, a clay, and a sandstone, showed good agreement between freezing and standard methods. The freezing technique described here has a water potential resolution of about -11 J kg-1. An entire characteristic can be determined within 24 hours
Characterization of particle-size distribution in soils with a fragmentation model
No full textParticle-size distributions (PSDs) of soils are often used to estimate other soil properties, such as soil moisture characteristics and hydraulic conductivities. Prediction of hydraulic properties from soil texture requires an accurate characterization of PSDs. The objective of this study was to test the validity of a mass-based fragmentation model to describe PSDs in soils. Wet sieving, pipette, and light-diffraction techniques were used to obtain PSDs of 19 soils in the range of 0.05 to 2000 μm. Light diffraction allows determination of smaller particle sizes than the classical sedimentation methods, and provides a high resolution of the PSD. The measured data were analyzed with a mass-based model originating from fragmentation processes, which yields a power-law relation between mass and size of soil particles. It was found that a single power-law exponent could not characterize the PSD across the whole range of the measurements. Three main power-law domains were identified. The boundaries between the three domains were located at particle diameters of 0.51±0.15 and 85.3±25.3 μm. The exponent of the power law describing the domain between 0.51 and 85.3 μm was correlated with the clay and sand contents of the soil sample, indicating some relationship between power-law exponent and textural class. Two simple equations are derived to calculate the parameters of the fragmentation model of the domain between 0.51 and 85.3 μm from mass fractions of clay and silt
Random process analysis with R
No full textRandom process analysis (RPA) is used as a mathematical model in physics, chemistry, biology, computer science, information theory, economics, environmental science, and many other disciplines. Over time, it has become more and more important for the provision of computer code and data sets. This book presents the key concepts, theory, and computer code written in R, helping readers with limited initial knowledge of random processes to become confident in their understanding and application of these principles in their own research. Consistent with modern trends in university education, the authors make readers active learners with hands-on computer experiments in R code directing them through RPA methods and helping them understand the underlying logic.
Each subject is illustrated with real data collected in experiments performed by the authors or taken from key literature. As a result, the reader can promptly apply the analysis to their own data, making this book an invaluable resource for undergraduate and graduate students, as well as professionals, in physics, engineering, biophysical and environmental sciences, economics, and social sciences
Comparison of soil water content estimation equations using ground penetrating radar
Full text linkSoil water content has an important impact on many fundamental biophysical processes. The quantification of soil water content is necessary for different applications, ranging from large-scale calibration of global-scale climate models to field and catchment scale monitoring in hydrology and agriculture. Many techniques are available today for measuring soil water content, ranging from point scale soil water content sensors to global scale, active and passive, microwave satellites. Geophysical methods are important methods, used for several decades, to measure soil water content at different scales. Among these methods, ground penetrating radar has been shown to be one of the most reliable and promising ones. Soil water content measurement using ground penetrating radar requires the application of parametric equations that will convert the measured dielectric permittivity to water content. While several studies have been performed to test equations for soil water content sensors such as time domain reflectometry, a few studies have been performed to test different formulae for application to ground penetrating radar. In this study, we compare available formulae for converting dielectric permittivity obtained from detailed laboratory scale measurement of reflected waves using ground penetrating radar. Four soils covering a wide range of textures were used and the measured soil water contents were compared with values obtained from gravimetric measurements. Results showed that the dielectric mixing model of Roth et al. (1990) provided the best fit for individual soil textural classes, except for sandy soils. However, for all data combined the dielectric mixing model performed much better with significant difference in coefficient and determination and root mean square error. Empirical equations developed from calibration of time domain reflectometry performed poorly when applied to estimation of soil water content obtained from ground penetrating radar. Differences in sample volume, frequency of operation and data analysis between ground penetrating radar and time domain reflectometry, suggest to use more flexible and robust electromagnetic mixing formulae, allowing for incorporating the dielectric properties of constituents materials and geometrical features of the media. Sensitivity analysis was then performed to provide detailed information for the most accurate application of the selected dielectric model. Sensitivity analysis showed that the geometric parameter α and the dielectric permittivity of the solid phase ∊s are the two most sensitive parameters, determining important variations in the estimation of soil water content. Based on these results, these two parameters are suggested as fitting parameters, to be selected if the model is fitted to data. Otherwise, the model can be successfully used without calibration, as presented in this study, by using α = 0.5 (as also suggested by the authors) and ∊s = 4, which is an average value for soil minerals
An empirical model for the evaluation of the degree of saturation of shallow soils in relation to rainfalls
No full textProcessi di interazione suolo-atmosfera su un pendio soggetto a frane superficiali: un caso di studio nell’Oltrepò Pavese
No full textDetailed analysis of soil-atmosphere interactions in two sample sites in Oltrepò Pavese
No full textLarge-scale quantitative assessment of water resources is generally carried out using models that take into
account the soil-atmosphere interaction and hydraulic behaviour of an unsaturated soil.
Volumetric water content and pore water pressure are the main basic characteristics to be considered when
assessing the hydraulic behaviour of the soil in relation to rainfall events. These quantities are very useful
because they constitute input data in different types of water balance models.
Some models require knowledge of water retention curves that indicate a sort of “biunivocal” link between
water content and pore water pressure. Most of these models include a single hysteresis, due to in situ wettingdrying
processes to which soils are subjected under natural conditions (Bordoni et al., 2017).
Experimental evidence shows that the “biunivocal” relationship between the quantities considered does not
allow to adequately reproduce the real behaviour of un saturated soils. In the modelling chain, this mismatch
can lead to an inappropriate estimate of water resources, in relation to the amount of rain.
This note reports a detailed description of the interaction between soil and atmosphere in a specific area in
Northern Italy. Data from continuous monitoring of two sample sites in Oltrepò Pavese, namely Montuè and
Costa Cavalieri, representing two different geological contexts, were used (Bordoni et al., 2015). Different
time spans have been considered, even those including single rainy events. Field measurements of both water
content and pore pressure allow to clearly identify not only the seasonal fluctuations of the hydraulic properties
of the soil, but also the hysteresis cycles that characterize the hydraulic behaviour of the unsaturated soil in
correspondence of single rain events. In order to achieve this objective, the data recorded over a long period of
time were processed and graphs representing the link between pore pressure and water content were obtained.
The trends were also compared with the data on precipitation and air temperature.
Analysis of the data shows that the dynamics characterising variations in water content and pore pressure
at both test sites are closely linked to the alternation of wet and dry periods. However, the response is different
in the two sample sites because it depends on the geological context and on the type of shallow soil. It seems
that the response is also affected by the presence of preferential flow paths, especially in cracked clayey soil.
In general, it can be observed that in winter and spring months, after rain events followed by a prolonged
drying period, the response of soil layers up to 0.6 m from ground level is faster than that of the underlying
layers. In fact, by increasing depth, the interaction between soil and atmosphere is delayed. Moreover, it is
evident that the soil behaviour is not characterized by a single wetting-drying hysteresis, but by numerous
cycles that correspond to different isolated rainy events
Errori nella misura della ritenzione idrica dei suoli: conseguenze sulla stima del drenaggio profondo
No full textReduction of transpiration through foliar application of chitosan
No full textIn this study, we investigate the potential of chitosan, a natural beta-1-4-linked glucosamine polymer, to reduce plant transpiration. Chitosan was applied foliarly to pepper plants and water use was monitored. Peppers were grown in pots in growth-chambers, where transpiration was measured by weighing pots. In an accompanying field study, water use was determined by monitoring soil moisture depletion with time domain reflectometry. An automated irrigation system replenished the water used each day. Plant biomass and yield were determined to calculate biomass-to-water ratios. Differences in canopy resistance between control and chitosan treated plants were analyzed with the aid of the Penman-Monteith equation. Scanning electron microscopy (SEM) and histochemical analyses demonstrated that chitosan induced closure of the plant's stomata, resulting in decreased transpiration. Foliar application of chitosan reduced water use of pepper plants by 26-43% while maintaining biomass production and yield. We suggest that chitosan might be an effective antitranspirant to conserve water use in agriculture. © 2001 Elsevier Science B.V
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